Is the extra credit sitting on your account for next time? Did you change plans manually on renewal day? You are going to have to reach out to the mods (you can use the chat bot on the lower right). If it is sitting on your account, it may not be refunded until next time you have to pay anyway (these things take time).
During the day until around 10pm eastern, they tend to be active. You can also try sending a private message by clicking here. (If it doesn't work, check to see if you are signed into the community).
